The alpha HAT was released in November 2015; sign up here to be one of the first to get a HAT platform. The HAT platform is initially available through two HAT Platform Service Providers (HPPs); EnableID for the UK and Europe, and Noggin Asia for Singapore and Asia. More HAT platform hosts will be coming soon in other countries so do watch this space.
The HAT is available to everyone free of charge, up to a degree of storage and depending on whom you choose as your HAT host. Also, the entire ontology, schema and database of the HAT is open-sourced and free for anyone to download and innovate with in line with its Creative Commons Attribution-NoDerivative licence.